personally, i'd go with lacto-fermentation as opposed to kefiring with any type of veggie. kefir grains eat milk sugars. of course, they can also eat sugars in fruits and coconut milk and loads of other liquids. however, i don't know if there are enough sugars in sea vegetables to keep the kefir happy. perhaps ground up into a slurry with a healthy load of added honey or other sweetener? it may be easier just to submerge the whole sea veggies in salty water and ferment it like kraut.

no experience here - just guesses. anyone ever tried?

please post your experiments here if you decide to try kefiring your veggies and let us know how it goes!